The present invention relates to an ultrasound inspection apparatus which images an inspection object, such as an organ in a living body, through transmission and reception of an ultrasonic beam to produce an ultrasound image for inspection or diagnosis of the inspection object, a signal processing method for an ultrasound inspection apparatus, and a recording medium having a program recorded thereon.
An ultrasound inspection apparatus using an ultrasound image has hitherto been put into practical use in the field of medicine. In general, this type of ultrasound inspection apparatus has an ultrasound probe equipped with a transducer array and an apparatus body connected to the ultrasound probe. An ultrasonic beam is transmitted from the ultrasound probe toward a subject, an ultrasonic echo from the subject is received by the ultrasound probe, and a reception signal corresponding to the reception of the ultrasonic echo is electrically processed by the apparatus body to produce an ultrasound image.
In the ultrasound inspection apparatus, when producing an ultrasound image, a reception signal (element data) received from each transducer of the ultrasound probe is subjected to delay time correction and signal synthesis (phasing and adding) to produce a sound ray signal, on the assumption that a sound speed in a living body of the subject is constant. Further, an ultrasound image is produced from the produced sound ray signal. However, there is variation in sound speed value in an actual living body, and due to the variation, spatial distortion arises in the ultrasound image.
Meanwhile, in recent years, in order to more accurately diagnose a region to be diagnosed in the subject, an imaging region is divided into a plurality of subregions, an appropriate sound speed value is measured for each subregion, and the distortion of image is corrected by producing an ultrasound image using the sound speed values measured (JP 2010-99452 A).
Moreover, it is conceived that, in the ultrasound inspection apparatus, data before producing an ultrasound image is stored, and after imaging for the ultrasound image ends, tissue characterization, improvement in image quality or the like is performed using the stored data.
For example, JP 2006-325955 A describes that RAW data which is data before scan conversion to image data is stored along with the image data, and after an ultrasound imaging ends, desired RAW data is searched for and used in order to obtain analysis data for diagnosis from such analyses as analysis for a speed image, analysis for a slope of speed change, distortion analysis, analysis for a displacement image, and the like.
The measurement of the sound speed value described in JP 2010-99452 A is performed at a predetermined timing, for example, for every several frames. If the measurement frequency is high, while the definition of the ultrasound image is improved, a required time for sound speed value calculation increases. For this reason, there is a problem in that real-time property of display of the ultrasound image is deteriorated. Moreover, in the measurement of the sound speed value, the more a region for measuring the sound speed value is segmentalized, the more the accuracy of correction is improved. Even in this case, however, a required time for sound speed value calculation increases, and accordingly, there is a problem in that real-time property is deteriorated.
Accordingly, as described in JP 2006-325955 A, it is thinkable to store data before image production so as to minimize the correction during ultrasound imaging and ensure the real-time property, and so as to perform detailed correction on the stored data or perform data analysis using the stored data after the ultrasound imaging ends.
However, the RAW data which is described in JP 2006-325955 A as data to be stored is data after phasing and adding the reception signal received from the ultrasound probe. For this reason, it is not possible to correct the sound speed value used in the phasing and adding of the reception signal, and to perform analysis for a sound speed value, distortion or the like with high accuracy.
If the reception signal (element data) before phasing and adding is stored, it is possible to perform correction of a sound speed value used in the phasing and adding of the reception signal or analysis for a sound speed value, distortion or the like with high accuracy. However, the amount of element data which is not subjected to processing such as phasing and adding is enormous. For this reason, in the conventional ultrasound inspection apparatus, element data received from the ultrasound probe is only stored temporarily, and the element data after being subjected to processing such as phasing and adding is sequentially deleted.